Fayyaz A. Memon

Performance of a large building rainwater harvesting system

Rainwater harvesting is increasingly becoming an integral part of the sustainable water management toolkit. Despite a plethora of studies modelling the feasibility of the utilisation of rainwater harvesting (RWH) systems in particular contexts, there remains a significant gap in knowledge in relation to detailed empirical assessments of performance. Domestic systems have been investigated to a limited degree in the literature, including in the UK, but there are few recent longitudinal studies of larger non-domestic systems. Additionally, there are few studies comparing estimated and actual performance. This paper presents the results of a longitudinal empirical performance assessment of a non-domestic RWH system located in an office building in the UK. Furthermore, it compares actual performance with the estimated performance based on two methods recommended by the British Standards Institute - the Intermediate (simple calculations) and Detailed (simulation-based) Approaches. Results highlight that the average measured water saving efficiency (amount of mains water saved) of the office-based RWH system was 87% across an 8-month period, due to the system being over-sized for the actual occupancy level. Consequently, a similar level of performance could have been achieved using a smaller-sized tank. Estimated cost savings resulted in capital payback periods of 11 and 6 years for the actual over-sized tank and the smaller optimised tank, respectively. However, more detailed cost data on maintenance and operation is required to perform whole life cost analyses. These findings indicate that office-scale RWH systems potentially offer significant water and cost savings. They also emphasise the importance of monitoring data and that a transition to the use of Detailed Approaches (particularly in the UK) is required to (a) minimise over-sizing of storage tanks and (b) build confidence in RWH system performance.

Rainwater harvesting: model-based design evaluation

The rate of uptake of rainwater harvesting (RWH) in the UK has been slow to date, but is expected to gain momentum in the near future. The designs of two different new-build rainwater harvesting systems, based on simple methods, are evaluated using three different design methods, including a continuous simulation modelling approach. The RWH systems are shown to fulfill 36% and 46% of WC demand. Financial analyses reveal that RWH systems within large commercial buildings maybe more financially viable than smaller domestic systems. It is identified that design methods based on simple approaches generate tank sizes substantially larger than the continuous simulation. Comparison of the actual tank sizes and those calculated using continuous simulation established that the tanks installed are oversized for their associated demand level and catchment size. Oversizing tanks can lead to excessive system capital costs, which currently hinders the uptake of systems. Furthermore, it is demonstrated that the catchment area size is often overlooked when designing UK-based RWH systems. With respect to these findings, a recommendation for a transition from the use of simple tools to continuous simulation models is made.

Environmental implications of water efficient microcomponents in residential buildings.

The Code for Sustainable Homes (CSH) in England sets out various water efficiency targets/levels, which form part of environmental performance criteria against which the sustainability of a building is measured. The code is performance based and requires reduction in per capita water consumption in households. The water efficiency related targets can be met using a range of water efficient microcomponents (WC, showers, kitchen taps, basin taps, dishwashers, washing machines, and baths). However, while the CSH aims at reducing the adverse environmental implications associated with the dwellings by promoting reduction in water consumption, little is known about the energy consumption and the environmental impacts (e. g. carbon emissions) resulting from water efficient end uses. This paper describes a methodology to evaluate the energy consumption and carbon emissions associated with the CSHs water efficiency levels. Key findings are that some 96% and 87% of energy use and carbon emissions, respectively associated with urban water provision are attributable to in-house consumption (principally related to hot water), and that achieving a defined water efficiency target does not automatically save energy or reduce carbon emissions.

Impacts of residence time during storage on potential of water saving for grey water recycling system.

Grey water recycling has been generally accepted and is about to move into practice in terms of sustainable development. Previous research has revealed the bacteria re-growth in grey water and reclaimed municipal water during storage. However, in most present grey water recycling practices, impacts of water quality changes during storage on the systems performance and design regulation have not been addressed. In this paper, performance of a constructed wetland based grey water recycling system was analysed by taking the constraint of residence time during storage into account using an object based household water cycle model. Two indicators, water saving efficiency (WSE) and residence time index (RTI), are employed to reflect the systems performance and residence time during storage respectively. Results show that WSE and RTI change with storage tank volumes oppositely. As both high WSE and RTI cannot be achieved simultaneously, it is concluded that in order to achieve the most cost-effective and safe solution, systems with both small grey and green tanks are needed, whilst accepting that only relatively modest water saving efficiency targets can be achieved. Higher efficiencies will only be practicable if water quality deterioration in the green water tank can be prevented by some means (e.g. disinfection).

Reliability Indicators for Water Distribution System Design: Comparison

AbstractWhen designing a water distribution system (WDS), it is imperative that the reliability of the network is taken into consideration. It is possible to directly evaluate the reliability of a WDS, although the calculation processes involved are computationally intensive and thus undesirable for some state-of-the-art, iterative design approaches (such as optimization). Consequently, interest has recently grown in the use of reliability indicators, which are simpler and faster to evaluate than direct reliability methods. In this study, two existing reliability indicators, the Todini resilience index and entropy for WDS, are examined by analyzing their relationships with different subcategories of reliability, namely the mechanical (network tolerance to pipe failure) and hydraulic reliability (network tolerance to demand change). The analysis is performed by generating comparable solutions through multiobjective optimization of cost against the chosen indicators using the well known Anytown WDS benchmar...

Harvested rainwater quality: the importance of appropriate design

This paper summarises the physicochemical and microbiological quality of water from a rainwater harvesting (RWH) system in a UK-based office building. 7 microbiological and 34 physicochemical parameters were analysed during an 8 month period. Physicochemically, harvested rainwater quality posed little health risk; most parameters showed concentrations below widely used guideline levels for drinking water. However, RWH system components (e.g. fittings and down pipes) appear to be affected soft water corrosion, resulting in high concentrations of some metals (copper, zinc and aluminium). This suggests the material selection of such fittings should be considered keeping in view the hardness of rainwater of an area. Microbiologically, Cryptosporidium, Salmonella and Legionella were not present in the samples analysed. However, faecal coliform counts were high at the beginning of the study, but did decrease over time in weak correlation with increasing pH. Enterococcus faecalis displayed counts consistently above UK rainwater harvesting standards. Inappropriate roof and rainwater good design, as well as material selection appear to be responsible for the reduced microbial quality, as they promoted contributions from avian sources and inhibited cleaning activities. Building and RWH system designs require greater consideration of local factors, which are critical for optimising harvested rainwater quality, to prevent both the development of contaminated sediments and health impacts.

Assessment of gully pot management strategies for runoff quality control using a dynamic model

A gully pot is the first entry point of road runoff into an urban drainage network. Pots are extensively used to trap solids from runoff in order to avoid/minimise the problems associated with sediment deposition in the downstream drainage structures or receiving waters. Here we briefly describe the different modules of a dynamic gully pot model developed to assess the impact of a series of management practice scenarios on the quality of runoff discharged through the pots. Runoff quality was modelled in terms of suspended solids (SS), chemical oxygen demand (COD), dissolved oxygen (DO) and ammonium. The model has the flexibility to represent the impact of various interactions between physical and biochemical processes occurring in a pot during wet and dry weather conditions, respectively. The simulation results show that the pots are effective at retaining solids, but their role with regard to reduction of dissolved pollutants is almost neutral. Model predictions, as against common perception, show that frequent pot cleaning does not significantly improve the runoff quality. However, considerably improved solid retention is possible if larger pots with modified geometry are introduced into the drainage system.

An integrated model to evaluate water-energy-food nexus at a household scale

To achieve a sustainable supply and effectively manage water, energy and food (WEF) demand, interactions between WEF need to be understood. This study developed an integrated model, capturing the interactions between WEF at end-use level at a household scale. The model is based on a survey of 419 households conducted to investigate WEF over winter and summer for the city of Duhok, Iraq. A bottom-up approach was used to develop this system dynamics-based model. The model estimates WEF demand and the generated organic waste and wastewater quantities. It also investigates the impact of change in user behaviour, diet, income, family size and climate.The simulation results show a good agreement with the historical data. Using the model, the impact of Global Scenario Group (GSG) scenarios was investigated. The results suggest that the fortress world scenario (an authoritarian response to the threat of breakdown) had the highest impact on WEF. Develop a model capturing the interactions between WEF at a household scale.The developed model can quantify WEF demand and the generated waste from a household.Explore the impact of change in user behaviour, income and seasonality on WEF.Sensitivity, uncertainty and comparison with historical data for model validation.Investigate the impact of future scenarios using the system dynamics-based model.

Constructed wetlands for urban grey water recycling

Three differently configured constructed wetlands: a Horizontal Flow Reed Bed (HFRB), Vertical Flow Reed Bed (VFRB) and a novel constructed wetland (the Green Roof Water Recycling System (GROW) patent number GB 2375761) were compared for treatment of weak organic strength domestic grey water for reuse over a period of nine months. Influent and effluent were characterized in terms of standard water quality parameters and also by size and hydrophobicity to determine the organic fractions of grey water targeted during treatment. All three wetlands achieved significant reduction in key pollutants ranging from 87?93% BOD5, 70?88% SS and 2.1?2.8 log reduction indicator microorganisms. Removal of pollutants occurred across a wide range of particle size. Hydrophilic organic fractions were preferentially removed compared to the hydrophobic components of the grey water.

Dynamic modelling of roadside gully pots during wet weather

Roadside gully pots form a common and important part of many surface water drainage networks. Their primary function is to retain larger solids from road runoff in order to minimise the problems associated with sediment deposition in downstream drainage structures and receiving waters. Typical processes occurring in pots during wet weather are dilution, dispersion, sedimentation, sediment bed build-up and erosion, washout of suspended and dissolved pollutants from the pot liquor and reaeration of the pot liquor. A dynamic water quality model has been developed to simulate these processes. To study the pollutant washout patterns and sludge bed erosion, simulated wet weather tests were carried out on pots draining six different types of roads. Results corroborated earlier findings and were used to successfully calibrate and verify the model.